Vitamin A and some of its analogs (retinoids) prevent the development of many chemically-induced epithelial tumors. The inhibition of transplantable tumors is stil questionable, although it has been demonstrated in several cases. Mechanisms of action of vitamin A either on normal cells or on tumor cells are unknown, and this is in part due to the lack of suitable in vitro systems which are necessary to establish the mechanism(s) by which retinoids exert their tumor inhibitory effects. We have demonstrated that two malignant murine melanomas, B16 and S91, are inhibited by low concentrations of retinyl acetate or retinoic acid in tissue culture. Furthermore, treatment of these tumor cells either before or after their injection into mice decreased their tumorigenicity. We propose to use these cell lines, grown in vitro, to determine the possible mechanisms for the uptake of retinoids, their internalization and intracellular compartmentalization. The presence of intracellular retinoid-binding proteins (RBP) will be tested, and if found, the retinoid-RBP complex will be partially purified and its ability to bind nuclear components (such as non-histone proteins or chromatin) will be investigated. Preliminary results have indicated possible alterations in cell surface components when cells are exposed to retinoic acid; we will use a variety of surface and metabolic labeling techniques to characterize the modified or "new" components. Detailed analyses of the biosynthesis of glycoproteins and glycosaminoglycans by cells exposed to retinoids will be performed. We will investigate the possible therapeutic use of retinoids in inhibiting tumor development in mice as well as on the fate of circulating tumor cells capable of metastatic spread. The information that will emanate from these studies will increase our understanding of the mechanism of action of retinoids and may establish whether retinoids could be used in the chemotherapy of certain tumors in vivo.